Missiles are often stored, transported and launched from the same cylindrical container. Over the course of inserting the missile into its launch container, transporting the container, storing the container, and launching from the container, the interface between the outside surface of the missile and the internal surface of the container experiences a variety of friction events. For example, the missile will experience rattling and shaking during transport from its production point to a silo. The missile and its container also experience environmental changes over time while the missile is in storage. In addition, the missile and container will experience extreme environmental changes (primarily extreme heat) upon missile egress.
The interface mechanism between the external surface of the missile, on the one hand, and the inside walls of the container, on the other hand, significantly impacts the performance and accuracy of the missile on egress. Consequently, the interface mechanism has the potential for being the critical design load condition for the missile and needs to accommodate various types of movement and temperature changes over the course of time. The interface design is based on requirements for manufacturing tolerances and changes in shape due to environments and/or missile motor operation. For example, over the life of the missile, a missile composite motor case may absorb moisture resulting in swelling of the motor case skin. As another example, at ignition, the high motor combustion pressure will cause the case to grow radially.
The interface design must be secure enough to ensure little or no rattling or shaking of the missile inside the container; must be capable of automatic adjustment to environmental changes, such as swelling of the motor case skin; and, at the same time, must be of sufficiently low friction such that the missile is unaffected by the interface during egress.
In the past, elastomeric pads were used to fill the annular rattle space between the missile and its container/launch tube. The pads, upon compression, would exert a force on the missile to return it to the central position. Currently, various forms and shapes of shims are still used as inserts between the missile and the container. However, the shims are not capable of adjustment to accommodate changes in the radius of the container, and they are limited in their ability to counteract the movement of the container that is in opposite force to the stationary missile contained within. In addition, if the shims are wedged in tightly in order to keep the missile from moving, the friction forces between the shims, the missile, and the container can adversely affect the missile performance due to friction forces upon egress.
Various forms of shims have been developed, yet they do not adequately address the dual requirements for reducing friction and minimizing vibration and movement. For example, U.S. Pat. No. 4,406,211 to Andersen discloses a shock absorbing system for missile containers comprising a plurality of shock pads and struts circumferentially and continuously adhesively bonded to the inside surface of the missile launcher. The continuous ring of pads and struts counteract lateral missile movement, but are not self-adjusting and are in almost continual circumferential contact with the missile thereby causing friction upon egress.
Accordingly, there is a need in the art for a shock absorbing apparatus with minimal interface between the missile and the container, that supports the missile circumferentially while minimizing rattle space, and which minimizes the static and dynamic friction forces at the same interface.